In order to reduce a spatter-removing step, which is a loss step in a welding process, reducing spatters is intended. A conventionally known method for this purpose is a consumable electrode type arc welding method for alternately generating a short-circuit state and an arc state while repeating a forward feed and a reverse feed at a welding wire feeding speed.
FIG. 9 is a diagram showing time waveforms of a wire feeding speed and a welding output with respect to a temporal change in a conventional arc welding control method.
For example, as an arc welding control method for welding by alternately generating a short-circuit state and an arc state while feeding a welding wire as a consumable electrode, the following method is known. In this method, a feeding speed controller and an output controller are used. The feeding speed controller controls a wire feeding motor such that a forward feed and a reverse feed are periodically repeated at a wire feeding speed. Upon receiving an increase/decrease signal from the feeding speed controller, the output controller performs control such that the welding output is low in the period during which the wire feeding amount is small and the welding output is high in the period during which the wire feeding amount is large as shown in FIG. 9. With this operation, in the short-circuit state, the releasing force resulting from the reduction of the wire feeding speed can be used to transfer the wire fusion mass. Thus, even when short-circuit current, which is a primary cause of spatters, is reduced, a stable short-circuiting transfer welding can be maintained (see Patent Literature 1, for example).
In a typical arc welding control, the following control is performed. A wire feeding speed corresponding to a set current is output as a fixed speed, and the welding current is output based on the welding voltage in the arc period such that the output voltage is matched with the set voltage.
According to the technique disclosed in Patent Literature 1, the welding output is increased or decreased by periodically repeating forward feed Z1 and reverse feed Z2 at a wire feeding speed as shown in FIG. 9. Thus, in the control method of setting the welding output low in the period during which the wire feeding amount is small and setting the welding output high in the period during which the wire feeding amount is large, a short-circuit period and an arc period occur at a fixed ratio in one short circuit cycle. This stabilizes the arc and thus can reduce spatters. However, it is considered difficult to match the welding voltage with the set voltage, with the use of a method for outputting the welding current based on the welding voltage, i.e. a typical constant voltage control in the arc period. This is because the arc period is fixed and thus the welding voltage needs to be controlled within a predetermined time period. Raising a gain in order to forcedly control the welding voltage causes large variations in the arc length, which can lead to an unstable arc. For these reasons, the stable control of welding current and welding voltage is difficult.